1. Field of the Invention
The present invention relates generally to a vapor generating method and an apparatus using the vapor generating method.
2. Related Background Art
There are known the CVD (Chemical Vapor Deposition) technique for supplying a compound gas of elements forming a thin film material to an object to be treated, such as a semiconductor wafer, to form a desired thin film by a chemical reaction in a vapor phase or on a wafer surface, and a drying technique for evaporating IPA (isopropyl alcohol) to allow the vapor gas to be in contact with an object to be treated (an object to be dried) to dry the object. In these CVD and IPA drying techniques, a vapor generating apparatus is used to generate a material gas and a dry gas.
The vapor generating apparatus uses: 1 a bubbling method for bubbling a liquid to be evaporated, by utilizing an ultrasonic wave and a carrier gas and for heating the liquid to a predetermined temperature to produce a gas to supply the gas together with the carrier gas to a processing chamber; 2 baking method for heating a liquid to be evaporated, which is contained in a heating tank or an evaporating dish, to produce a gas to transport the gas using its vapor pressure and for supplying a predetermined amount of gas to a processing chamber by means of a high-temperature mass flow controller; or 3 a direct injection method for allowing a liquid to be evaporated, which is transported by a pump, to pass through a gap between an orifice part and a diaphragm surface to vaporize the liquid and for heating the liquid to produce a gas to supply the gas to a processing chamber.
However, in the case of the bubbling method 1, there are many control factors to produce a predetermined gas, and it is required to perform strict temperature control in order to gasify the liquid to be evaporated. In addition, it is required to use a great amount of carrier gas, and there is a problem in that the quantitative ability and repeatability are not sufficient in accordance with the variation in consumption of the liquid to be evaporated (material).
In the case of the baking method 2, it is required to utilize the vapor pressure of the liquid to be evaporated (material) to perform the flow control by means of the high-temperature mass flow controller, and it is required to use a predetermined capacity of heating tank or evaporating dish, so that the structure is complicated and large. Thus, the costs are increased and there is a limit to the degree of freedom for designing the system. In addition, although the baking method has a smaller number of control factors in comparison with the bubbling method, since the baking method uses a low vapor pressure material, the produced pressure is low even if the low vapor pressure material is heated, so that there is a problem in that it is difficult to obtain a pressure required to stably transfer the vapor.
In addition, since the direct injection method 3 transports the liquid to be evaporated, in a liquid state to directly vaporize the liquid near a treatment part to perform the flow control, the direct injection method has a smaller number of control factors in comparison with the bubbling method and the baking method, and the size of the system can be decreased. However, since the direct injection method can cope with only a small amount of produced gas, there is a problem in that there is a limit to the use.